Two-horse chariot races (bigae) were held in the Campus Martius, the area of Rome named for Mars, after which the right-hand horse of the winning team was transfixed by a spear, then sacrificed. The horse’s head (caput) and tail (cauda) were cut off and used separately in the two subsequent parts of the ceremonies: two neighborhoods staged a fight for the right to display the head, and the freshly bloodied cauda was carried to the Regia for sprinkling the sacred hearth of Rome.
Alrighty then
Became familiar with the term with Colleen McCulloughs books of Rome series. Excellent book series.